Conductive carbon materials, such as acetylene black, carbon nanofibers (hereinafter referred to as “CNF”) and mixtures thereof, have been used as a filler for imparting conductivity to resins, or a conductive additive for electrodes of various batteries, particularly lithium ion batteries. In particular, CNF is one of the most promising of the conductive carbon materials since a relatively small amount of CNF can impart great conductivity to a target. CNFs have a fibrous shape, and generally have 5 to 100 nm of the outer diameter and 10 or more of the aspect ratio. Note that the aspect ratio means the ratio of the length to the outer diameter of fiber.
CNFs have been manufactured by various processes such as arc discharge method, catalytic chemical vapor deposition method, and laser ablation method. Among them, the catalytic chemical vapor deposition method would be the most preferred as an industrial manufacturing process. The catalytic chemical vapor deposition method uses transition metal particles as a catalyst, and contacts the catalyst with a source gas which is the carbon source, such as acetylene and benzene gas, to grow CNF from the catalyst particles at a high temperature, e.g., 900 degrees C. or more in general. It has been focused on a process for producing CNF from a source gas composed mainly of carbon monoxide using a transition metal ingredient such as cobalt as a catalyst since the process is considered to be able to produce CNF with high purity and quality at a relatively low temperature (see Patent Documents 1 to 5).